Steering networks are networks that accept signals from a large plurality of signal sources and steer, or switch, those signals in accordance with some aim, generally to desired destinations. The plurality of sources is generally one where not all of the sources are active at any one time, and the destinations are generally paths or service providing equipment. Steering is useful when the number of paths or the number of service providing equipment is smaller than the number of sources, and where it is not critical to which one of the paths or service providing equipment the connection is made. Because the sources dynamically share access to the destinations on a demand basis and because the number of destinations is smaller than the number of sources, steering is a form of concentration. Thus, many concentration functions are implemented with steering networks.
In many steering and concentration applications the required processing occurs mostly during the service request period, as contrasted with the information communication period. In such applications, time delay to achieve the steering and concentration is not critical because incoming requests generally require neither immediate nor simultaneous response to all incoming requests. In consequence of this insensitivity to delay, prior art steering networks characteristically employ sequential operation. The steering network's circuitry sequentially monitors all incoming lines and when a service request is detected, the line requesting service is connected to an available one of a plurality of paths or service providing equipments. This approach is too slow for high speed steering applications.
Recent advances in high speed switching can not fully realize their potential without new techniques and arrangements for steering information within switching systems so that the switching system processors can operate both quickly and efficiently. The steering circuits internal processing should therefore be arranged to optimize the efficiency of the overall processing of the switching system.
In a copending application, entitled "Self-Routing Switching Network" and filed on even date herewith, A. Huang and I have disclosed a wide band, full access, self routing switch that is adapted to a packet switching environment. In a packet switching environment, information is processed, moved, and otherwise handled in short bursts, or packets. Each packet contains an activity bit to indicate whether the packet contains information or is empty (a "0" or a "1", respectively, for example) followed by an address field which may comprise a number of subfields (most significant bits first). The address field is followed by an information field which carries the data. All packets are synchronized so that the processing equipment can operate on many packets simultaneously. The simultaneous and synchronous operations within the self routing switch makes speed and parallel operation necessary attributes of the components that make up the switching network. Other attributes which are desirable are modularity and distributed control.
For efficient utilization of the self routing switch in applications where there are many potential users of the switch but only a small number of active users at any one time, in my copending application we have concluded it to be advantageous to include a steering network to serve as a preprocessing concentrator. However, the requirement of simultaneous and synchronous operation could not be satisfied by prior art steering networks or concentrator networks because of their sequential operation characteristic.
Herein is disclosed a steering network architecture that possesses the desired attributes of speed and parallel operation, permitting the realization of a concentrator stage for a packet-switching, self routing, full access switching network.